Carboxy-terminated butadiene-vinyl ferrocene copolymers

ABSTRACT

Copolymers of butadiene and vinyl ferrocene (VF) are disclosed along with preparative procedures therefor. The copolymers are produced in an organic solvent when polymerization is initiated by a carboxy-containing azo compound, such as, azobis(2-methyl-4carboxy butyronitrile), thereby forming a copolymer of butadiene and vinyl ferrocene. The copolymers are useful in propellant formulations as a binder where high buring rates are desired.

145] May 27, 1975 1 1 CARBOXY-TERMINATED BUTADlENE-VINYL FERROCENE COPOLYMERS [75] Inventor: Samuel F. Reed, Jr., Holland, Pa.

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

22 Filed: Dec. 7, 1970 211 App]. No.: 95,889

[52] US. Cl. 260/439 CY; 260/821 [51] Int. Cl C08d 3/06 [581 Field of Search 260/439 CY, 82.1

[56] References Cited UNITED STATES PATENTS 3,518,241 6/1970 Duling 260/895 3,586,552 6/1971 Potts et a1. 149/20 X 3,718,633 2/1973 Baldwin et a1. 149/19 X FOREIGN PATENTS OR APPLICATIONS 601,243 7/1960 Canada 260/439 CY OTHER PUBLICATIONS Baldwin et al. I, Chem. Abs, 67, No. 82412 f, (1967),

QDl A51.

Bamford et al., Trans. Faraday Soc., 56, 932-942, (1960), TK I F 25.

Asimoto et al., .I. Am. Chem. Soc., 77, 6295-6297, (1955), QD l A 5.

Pittman, .I. Polymer Science, P.B., 6, 1921, (1968), OD 281 p6 J62.

Primary ExaminerBenjamin R. Padgett Assistant Examiner-E. A. Miller Attorney, Agent, or Firm-Robert P. Gibson; Nathan Edelberg; William P. Murphy [57] ABSTRACT Copolymers of butadiene and vinyl ferrocene (VF) are disclosed along with preparative procedures therefor. The copolymers are produced in an organic solvent when polymerization is initiated by a carboxycontaining azo compound, such as, azobis(2-methyl-4- carboxy butyronitrile), thereby forming a copolymer of butadiene and vinyl ferrocene. The copolymers are useful in propellant formulations as a binder where high buring rates are desired.

1 Claim, No Drawings CARBOXY-TERMINATED BUTADIENE-VINYL FERROCENE COPOLYMERS BACKGROUND OF THE INVENTION additives for this purpose, usually in the form of liquids 1 which also serve as plasticizing agents. In the liquid state the ferrocenes display the inherent disadvantages characteristic of liquid additives, such as loss by evaporation, migration, etc., and consequently, the propellant systems suffer, particularly on long term storage.

Thus, a need exists for a modified form of ferrocene additive which form is not subject to being lost by evaporation or migration from a stored propellant composition.

An object of this invention is to combine the ferrocene additive with the binder being utilized in the propellant system.

Another object is to combine a ferrocene derivative and a binder material via a polymerization technique into a serviceable prepolymer suitable for propellant mixing and curing.

A specific object of this invention is to copolymerize a binder material and a catalyst material to provide a liquid copolymer which is capable of undergoing a cure reaction when used in a propellant composition to form a rubber-like binder material having a burning rate catalyst agent as an integral part thereof.

SUMMARY OF THE INVENTION Vinyl ferrocene is copolymerized with butadiene in an inert organic solvent after the polymerization reaction is initated by a carboxy-containing azo compound, such as, azobis(2-methyl-4-carboxy butyronitrile). The liquid copolymer is characterized by its molecular weight which is in the range of from about 1,000 to about 10,000, its carboxy-end group content from about 0.5 weight percent to about 9 weight percent, and its iron content from about 0.5 weight percent to about weight percent. The liquid copolymer is capable of undergoing a cure to a final rubber-like state.

DESCRIPTION OF THE PREFERRED EMBODIMENT The copolymer formed by reaction of butadiene with vinyl ferrocene is useful as a combination binder and burning rate catalyst for solid propellant compositions.

The liquid copolymer is characterized by its preferred molecular weight range from about 1,000 to about 10,000, its preferred carboxy-end group content from about 0.5 weight percent to about 9 weight percent, and its iron content from about 0.5 weight percent to about 15 weight percent. The liquid copolymer of butadiene-vinyl ferrocene is produced by a procedure as described by the descriptive technique set forth below as Example I. Table I below sets forth the experimental data on preparation of butadiene-VF copolymers. Table 11 below, sets forth the physical property data for butadiene-VF copol ymers produced with the concentrations set forth in Table I.

The butadiene-VF mole ratios may vary from approximately 100:1 to about 1:1. The ratio of 1:1 yields a copolymer with an iron content of about 15 weight percent. The organic solvents wherein copolymerizations are conducted may be toluene or dioxane. Polymerization temperatures may conveniently be maintained in the range of -80C. Reaction times may vary over the range of 24-120 hours; however, a reaction time in the range of about 72 hours is preferred.

Copolymers having molecular weights ranging from about 1,000 to about 10,000,. carboxy-end group contents of from about 0.5 to about 9 weight percent of the copolymer, and an iron content from about 0.5 weight percent to about 15 weight percent of the copolymer are easily obtained by varying the reaction conditions and concentrations of reactants and initiators. Other representative carboxy-containing azo compounds such as 4,4-azobis-(4-cyanovaleric acid), 3,3- azobis(3-cyanobutyric acid), and 2,2-azobis(2- cyanopropionic acid) may be employed as initiators for the polymerizations of this invention.

EXAMPLE I PROCEDURE FOR POLYMERIZATION OF BUTADIENE AND VINYL FERROCENE To a glass high-pressure reactor (aerosol tube) are introduced 30 ml. of dioxane, 1.0g (0.00465 mole) VF, and 326g (0.0196 mole) azobis(2'methyl-4-carboxybutyronitrile). The reactor is attached to a vacuum line and deaerated by three alternate freeze-thaw cycles. At this point 19.0g (0.352 moles) of butadiene are condensed into the reactor. The reactor is removed from the vacuum line and placed in an oil bath at 6667C. Heating is continued for a period of 72 hours. After cooling, the reactor is vented, the solvent removed by evaporation and the copolymer reprecipitated by dissolving in ether followed by the addition of methanol. After decanting the solvents, copolymer is stripped of excess solvents on a rotatory evaporator and finally dried at -75C. under reduced pressure (1 mm. Hg) for a period of 25 hours. The yield of copolymer is 11.2g (56 percent). Evaporation of the decanted solvents gave an additional 5.0g of the copolymer containing the low molecular weight copolymer and impuri- .ties. The liquid copolymer (methanol insolubles) is characterized by its molecular weight (4,100), carboxy-end group content (2.61 weight percent) and elemental analysis (percent FE-0.63 percent).

TABLE I Experimental Data on Preparation of Butadiene-VF Copolymers Weight No. Butadiene (B) VF Ratio Initiator Weight Yield (g/mmole) (g/mmole) B/VF (mmole) Copznlymer TABLE 11 Physical Property Data for Butadiene-VF Copolymers Calculated CO H weight 71 made on the basis of two CO H groups per chain for the molecular weight values reported.

Calculated Fe content made on the basis of the ratio of comonomers initiallycharged into the reactor.

The copolymers of this invention may be used as the binder-catalyst for a solid propellant composition. The copolymers may be used in the propellant composition in amounts from about 5 weight percent to about 30 weight percent. The remaining propellant ingredients exclusive of processing aids (such as lecithin) and trace amounts of other additives (e.g., stabilizing, ballistic, special curative, and the like) may be comprised of a plasticizer such as isodecyl pelargonate, a metal fuel such as aluminum, and an inorganic oxidizer such as ammonium perchlorate.

An example of a propellant composition using the copolymers of this invention is set forth under Example 11 below.

The burning rate for the propellant formulation of Example 11 compared with a standard containing only butadiene, as binder, is higher by about percent. The propellant formulation of Example II does not require an additional burning rate catalyst, and the formulation may be varied to incorporate a higher binder content and a higher iron content. The iron content may also be controlled by the amount of vinyl ferroamount of copolymer selected for use in the formulations. Those skilled in the art will recognize that the other propellant ingredients may be varied to include metal additives (e.g., aluminum powder or other powdered metals used in the art) in amounts from about 5 to about 20 weight percent, inorganic oxidizer such as, ammonium perchlorate from about 10 to about 72 weight percent. Other plasticizers may be used with the copolymers of this invention. Among the important plasticizers are nonvolatile organic liquids or low melting solids, especially the phthalic, adipate, and sebacate esters, and aryl phosphate esters. Plasticizer content is determined by the desirable properties required for a propellant formulation. Generally, plasticizer amounts from about 5 to about 30 weight percent is the range meeting most requirements. Special processing aids such as lecithin and trace amounts of additives known in the art for their specific contributions to the ballistic, castibility, and storage properties of the propellant may be added to the propellant formulation.

1 claim:

1. The carboxy-terminated copolymers of butadiene and vinyl ferrocene prepared by the method comprising reacting vinyl ferrocene and the initiator azobis(2- methyl-4 carboxy butyronitrile) in an inert organic solvent with butadiene at a reaction temperature and for a reaction time period sufficient for said reaction to take place after which solvent removal is effected and said copolymers are dried at a suitable drying temperature while under reduced pressure; said inert organic solvent being selected from dioxane and toluene; said reaction temperature being in the range of about 60 to about 80C; said reaction time being from about 24 hours to about 120 hours; said drying is accomplished at a suitable temperature in the range of about 70 to about 75C; said reduced pressure is in the range of about 1 millimeter; said reacting butadiene and vinyl ferrocene in mole ratios from approximately 100:1 to

cene copolymerized with butadiene as well as the 1:1 to form said copolymers characterized by a molecular weight in the range from about 1,000 to about 10,000, carboxy-end group content of about 0.5 weight percent to about 9 weight percent, and an iron content of about 0.5 weight percent to about 15 weight percent. 1 =l 

1. THE CARBOXY-TERMINATED COPOLYMERS OF BUTADIENE AND VNIYL FERROCENE PREPARED BY THE METHOD COMPRISING REACTING VINYL FERROCENE AND THE INITATOR AZOBIS(2-METHYL-4 CARBOXY BUTYRONITRILE) IN AN INERT ORGANIC SOLVENT WITH BUTADIENE AT A REACTION TEMPERATURE AND FOR A REACTION TIME PERIOD SUFFICIENT FOR SAID REACTION TO TAKE PLACE AFTER WHICH SOLVENT REMOVAL IS EFFECTED AND SAID COPOLYMERS ARE DRIED AT A SUITABLE DRYING TEMPERATURE WHILE UNDER REDUCED PRESSURE; SAID INERT ORGANIC SOLVENT BEING SELECTED FROM DIOXANE AND TOLUENE; SAID REACTION TEMPERATURE BEING IN THE RANGE OF ABOUT 60* TO ABOUT 80*C; SAID REACTION TIME BEING FROM ABOUT 24 HOURS TO ABOUT 120 HOURS; SAID DRYING IS ACCOMPLISHED AT A SUITABLE TEMPERATURE IN THE RANGE OF ABOUT 70* TO ABOUT 75*C; SAID REDUCED PRESSURE IS IN THE RANGE OF ABOUT 1 MILLIMETER; SAID REACTING BUTADIENE AND VINYL FERROCENE IN MOLE RATIOS FROM APPROXIMATELY 100:1 TO 1:1 TO FORM SAID COPOLYMERS CHARACTERRIZED BY A MOLECULAR WEIGHT IN THE RANGE FROM ABOUT 1,000 TO ABOUT 10,000, CARBOXY-END GROUP CONTENT OF ABOUT 0.5 WEIGHT PERCENT TO ABOUT 9 WEIGHT PERCENT, AND AN IRON CONTENT OF ABOUT 0.5 WEIGHT PERCENT TO ABOUT 15 WEIGHT PERCENT. 